The invention of this application is directed to the problem of providing such an engine mount with simple means which meet the requirement that oscillations of the engine casing be hydraulically damped by the engine mount when such oscillations are of low frequency and relatively great amplitude, and that high frequency oscillations with relatively small amplitudes of, for example, 0.1 mm remain hydraulically undamped as far as possible, whereby the vehicle frame or related engine supporting elements will not be loaded with hydraulic damping stresses.
Engine mounts of the type to which the instant invention relates generally comprise a first metallic end wall for connection to an engine casing, a second metallic end wall spaced axially from the first wall, a metallic supporting element for connection to an engine supporting frame, a first elastic rubber-like peripheral wall adheringly connected with the first end wall and with the supporting element, a partition connected with the supporting element so as to define with the first end wall and the first peripheral wall a liquid-filled main chamber of variable volume on one side of the partition, a second elastic rubber-like peripheral wall adheringly connected with the second end wall and with the supporting element so as to define an auxillary liquid-filled chamber of variable volume on the other side of the partition, means such as perforations or choke openings defining a flow connection between the main and auxiliary chambers, and means rigidly connecting the first and second end walls together for joint movement relative to the supporting element.
In one approach taken by the instant invention, there is disposed in the partition an annular member forming choke openings or connections between the main chamber and the auxiliary chamber, the annular member being disposed so as to be axially movable with reference to the partition and being limited in its stroke in the middle of the partition. Preferably the stroke of the annular member through the middle of the partition is such that the stroke volume of the annular member (the axially facing surface area of the annular member multiplied by the stroke distance) corresponds to the displacement volume of the liquid filled chambers with a total oscillation path of the engine mount of up to 0.2 to 0.3 mm. In this way, the engine oscillations up to this range cause substantially no liquid exchange between the chambers, but rather only a shifting or stroke of the annular member, whereby advantageously only a very small shifting force results, acting indirectly via the rubber-elastic peripheral walls on the metallic supporting element, because the mass of the annular member can be very small. With increasing oscillation paths, there is a gradual exchange of liquid between the main chamber and the auxiliary chamber that exerts damping forces, until with oscillation paths of, for example, 5 mm or more, strong damping forces are established by the flow resistance of the choke openings.
Advantageously a plate-like annular member is surrounded by an inwardly opening groove in the partition, whereby the groove flanks form impact surfaces, or alternatively the annular member is provided with U-shaped outwardly directed flanges that extend to impact surfaces on the partition. Here the impact surfaces of the partition and of the annular member may simply constitute tight contact surfaces in a stroke-limited state. If the annular member in non-stroke-limit positions presents free annular gaps with respect to the partition, the annular member can oscillate undamped between the impact surfaces of the annular member and the partition, and also the possible exchange of volume between the chambers can additionally suppress or ameliorate the occurrence of hydraulic damping forces at small amplitudes. The choke openings can be provided directly in a plate-like annular member, or in an intermediate wall of the annular member. Advantageously the annular member has only one choke opening which determines flow resistance with its full cross-section, or forms an annular cross-section that determines flow resistance with a bolt that connects the end walls. The intermediate wall of the annular member that is provided with a choke opening, or the whole annular member, can be made of a rubber-elastic material, whereby the choke opening may present a lip-like edge with a flow profile of special configuration turned toward the opening, which edge portion can be deformed by the flow forces to effect an enlargement or a reduction of the flow cross-section and a change of the throughput coefficient. Thus the flow resistance of the choke opening can be influenced or varied as desired, with increasing liquid exchange between the two chambers.
The annular member can be joined to the partition by a thin elastic flange, whereby also the deformation strength of the flange can limit the stroke of the annular member.
If an annular member penetrated by a connecting bolt presents a free annular gap and/or at least a resilient lip of elastic material in the region of the choke opening, there is achieved the advantage of ready transverse mobility of the walls that are rigidly joined by the connecting bolt, with reference to a partition that has little resilience.
In another aspect of the instant invention, the previously mentioned problem is solved by providing in one or both end walls openings or perforations that are covered by resilient wall parts which pose a decreasing resistance to a change of the fluid pressure in the appurtenant chamber, that is, the main chamber or the auxiliary chamber. Otherwise stated, these resilient wall parts are initially flexible so as to compensate for any volume change in the chamber, and hence resist a change of fluid pressure in the chamber, but thereafter the resilient wall parts reach the limit of their resilience so as not to compensate further or to the same degree to volume changes of the chamber, such that the fluid pressure in the chamber will rise rapidly. Thus the volume changes in the chambers per unit of time, at low amplitudes and high frequencies, are compensated by a corresponding movement of the resilient wall face parts without the need for any liquid exchange worth mentioning to occur through the choke opening, whereas at large amplitudes and low frequencies the volume changes or liquid volumes forced per unit of time, which volumes may be of the same total magnitude, will only in small part be taken up by the resilient wall parts, and the essential portion of the liquid must flow exclusively through the choke opening as soon as the resilient wall parts have respectively reached a limit of their yielding.
By the measures provided by this aspect of the invention, advantageously at small amplitudes and high frequencies the pressure building up in the chambers can be kept low by an appropriate dimensioning and configuration of the resilient end wall parts, and hydraulic damping will therefore be slight or insignificant, whereas at large amplitudes with low frequencies the pressure that is building up can be kept relatively high by suitable dimensioning and configuration of the choke opening, and hence hydraulic damping to the required degree will be attained.
In the inoperative state of an engine mount in accordance with the second aspect that is ready for operation, the chambers advantageously are at a pressure that is at or only slightly above or below atmospheric pressure. Then, if one considers approach of the end wall on the engine side to the supporting element to be the compression stage, and retreat of the said end wall from the supporting element to be the suction stage, with large volumes, evoked by large amplitudes in the compression stage only in the main chamber and in the auxiliary chamber only in the suction stage, pressure differences will occur that are determined by the actual flow resistance of the choke opening, the differences moving the resilient wall parts outwardly, while the auxiliary chamber in the compression stage and the main chamber in the suction stage will retain essentially the initial pressure. Consequently in both chambers there will only be slight pressure differences that tend to move the resilient wall parts inwardly.
Advantageously the resilient wall parts are made as diaphragms that are tightly joined with the edges of the openings or perforations in the end walls. The resilient wall parts can be made especially simply if a perforated wall face and rubber elastic diaphragms are adheringly joined at the edges of the perforations, forming a vulcanized rubber metallic part. The diaphragms can be made so that they are substantially flat in the dynamic middle portion of an operational engine mount. As soon as a diaphragm of suitable dimensions and configuration is bulged more strongly outwardly or inwardly from the basic position, the deformation strength or resistance thereof increases progressively, and, with large amplitudes, it can build up the desired pressure in the chambers. If the deformation strength of a diaphragm or other resilient wall part is inadequate for this purpose, simple mechanical ancillary means can reenforce the resistance of the resilient wall part with respect to the occurring pressure difference, e.g., a plate connected with the end wall can constitute an impact surface which limits the give of the diaphragm or similar part, after a predetermined stroke. The resilient wall parts may also be made as diaphragm parts applied to the inner side of a perforated wall face, whereby advantageously a diaphragm that covers the whole inside may lie freely on the wall face or be adheringly joined thereto. Material for diaphragms of this kind may also be a foamed material, especially polyurethane, made up of individual bubbles, whereby the resilience of the diaphragm with reference to the perforations or openings and the intrinsic resilience of the foamed material are summed, and acting together in case of high frequency oscillations and low amplitudes they compensate the volumes forced in the chambers, or the volume changes of the chambers. If such a foamed diaphragm is provided on the liquid side with a thin metallic or plastic foil, gas or liquid exchange between the individual bubbles and the appurtenant chamber can be reliably avoided, and it can even be prevented that a diaphragm without a foil will be punched through the perforations if the pressure in the chamber becomes increasingly high.
In general it is advantageous to equip both end walls of the engine mount with resilient wall parts in order to be able to compensate forced volume changes at low amplitudes and high frequency oscillation. If the elastic peripheral wall on the engine side essentially determines the elastic bearing capacity of the engine mount, and the peripheral wall away from the engine is so resilient that by corresponding deformation it can compensate the forced volumes in case of small amplitudes and high frequencies, it suffices to provide resilient wall parts only for the end wall toward the engine. There may be other reasons also for equipping only one end wall with resilient wall parts according to the invention, particularly if other supplementary measures of some other kind are provided for the engine mount to suppress hydraulic damping with high frequency oscillations and low amplitudes. It should be observed that quite generally other measures which are frequency or amplitude dependent may be combined with the invention to reinforce the effect described here, to influence the damping in the desired way, for other characteristic frequency/amplitude ranges, e.g., to reenforce them or to reduce them.
Other features, advantages and aspects of the invention will become apparent to those skilled in the art from the ensuing description of preferred embodiments, taken in conjunction with the accompanying drawings .